# Python and probability

This is a notebook for practicing Python and testing some probability problems.

# Things to remember Python vs R

Python indents and spacing matter
Python no curly braces in functions
Python is 0 indexed
Python can multiply strings Python is left inclusive and right exclusive
Python is object oriented Python “.” are important
Python pass objects to functions and use methods on objects
Lists and dictionaries are important
Create list with []
Create dictionary to store key:value pairs with {}
Use numpy for arrays and matrices
Use pandas for dataframes

# Functions

I will start by creating some functions for counting combinations and permutations.

``````# Use a package for factorial

import math

print(math.factorial(4)) # Must explicitly call print in Python``````
``````# Create a function for combinations

def combination(n, k = 2): # No curly braces, indentation and whitespace matter
""" Insert text here"""
combinations = math.factorial(n) / ((math.factorial(n - k)) * math.factorial(k))
return combinations # No automatic return, must be explicit
``````
``````# Test the combination function

print(combination(2)) # From 2 choose 2, order doesn't matter

print(combination(3)) # From 3 choose 2, order doesn't matter

print(combination(4)) # From 4 choose 2, order doesn't matter

print(combination(5)) # From 5 choose 2, order doesn't matter

print(combination(5,3)) # From 5 choose 3, order doesn't matter``````
```1.0
3.0
6.0
10.0
10.0```
``````# Create a function for permutations

def permutation(n, k = 2): # No curly braces, indentation and whitespace matter
""" Insert text here"""
permutations = math.factorial(n) / math.factorial(n - k)
return permutations # No automatic return, must be explicit
``````
``````# Test the permutation function

print(permutation(2)) # From 2 choose 2, order does matter

print(permutation(3)) # From 3 choose 2, order does matter

print(permutation(4)) # From 4 choose 2, order does matter

print(permutation(5)) # From 5 choose 2, order does matter

print(permutation(5, 3)) # From 5 choose 3, order does matter``````
```2.0
6.0
12.0
20.0
60.0```

# Applying function to a list

I want to create a list of combinations and a list of permutations.

``````# Create list of numbers and amount to be chosen

number_list = list(range(2, 11)) # Numbers from 2 to 10
choose_list =  * 9 # Number 2 repeated 9 times``````
``````print(number_list)
print(choose_list)``````
```[2, 3, 4, 5, 6, 7, 8, 9, 10]
[2, 2, 2, 2, 2, 2, 2, 2, 2]```
``````# Run combination function across all numbers in number_list - FOR LOOP METHOD

combinations_list_forloop = [] # Create an empty list

for x in number_list:
combinations_list_forloop.append(combination(x))
print(combinations_list)
``````
`[1.0, 3.0, 6.0, 10.0, 15.0, 21.0, 28.0, 36.0, 45.0]`
``````# Run combination function across all numbers in number_list - COMPREHENSION METHOD

combinations_list_comprehension = [combination(x) for x in number_list]

print(combinations_list_comprehension )
``````
`[1.0, 3.0, 6.0, 10.0, 15.0, 21.0, 28.0, 36.0, 45.0]`
``````# Run combination function across all numbers in number_list - MAP METHOD

combinations_list_map = list(map(combination, number_list))
print(combinations_list_map)``````
`[1.0, 3.0, 6.0, 10.0, 15.0, 21.0, 28.0, 36.0, 45.0]`

# Create a data frame

``````# Create the desired columns

column_1 = number_list
print(column_1)

column_2 = list(map(combination, number_list))
print(column_2)

column_3 = list(map(permutation, number_list))
print(column_3)``````
```[2, 3, 4, 5, 6, 7, 8, 9, 10]
[1.0, 3.0, 6.0, 10.0, 15.0, 21.0, 28.0, 36.0, 45.0]
[2.0, 6.0, 12.0, 20.0, 30.0, 42.0, 56.0, 72.0, 90.0]```
``````# Import pandas

import pandas as pd``````
``````# Create data frame containing combinations and permutations - DICTIONARY METHOD

probability_df = pd.DataFrame({
"Number": column_1,
"Combinations": column_2,
"Permutations": column_3})``````
``print(probability_df)``
```   Number  Combinations  Permutations
0       2           1.0           2.0
1       3           3.0           6.0
2       4           6.0          12.0
3       5          10.0          20.0
4       6          15.0          30.0
5       7          21.0          42.0
6       8          28.0          56.0
7       9          36.0          72.0
8      10          45.0          90.0```